CM47LE Owner's Manual

CM47LE OWNER'S MANUAL

Thank you for purchasing the Advanced Audio CM47LE tube condenser microphone. We have gone to great lengths to duplicate the audio sound signature of the original U47 tube circuit and capsule.

The CM47LE is a vacuum tube, large diaphragm, transformer coupled microphone, based on the classic U47 that has been used on countless hit records for the last 70 years including the Beatles.

The CM47LE is designed for pro studio, home studio, live, and broadcast applications.   It exceeds at capturing vocal performances but is equally at home on, guitars, acoustic/electric bass, instrument amplifiers,  piano, brass/woodwind instruments, strings, full orchestras and choirs .

The  U47 became extremely popular during the birth of pop music and is still sort after today for its ability to capture folk, pop/rock, jazz or country vocals . U47 microphones are still widely used today in professional recording studios around the world.   Properly working original U47 microphones have become very rare and extremely expensive to acquire.

The CM47LE is a perfect reproduction of the original U47 but with brand new high quality components and exacting attention to subtle details of the U47. 

INTRODUCTION

The CM47LE was created to offer the classic signature sound and circuit design of the U47 to a new generation of recording artists, producers and engineers at an an extremely affordable price.

We have nearly 50 years of experience listening to and recording with tube microphones and we have most likely auditioned over two dozen different U47 microphones in that time span.  We maintained a 1952 and 1959 U47 for nearly 20 years during my tenure at Ocean Sound Studios.

We decided to build one that compared to a late1958/1959 U47 like the one we had through-out the 70's and into the 90's at Ocean Sound.

The 1952 version had an older version transformer that rolled out the low end a bit early to our ear.  Plus, we prefer the consistency and quieter performance of the K47 capsule which was skinned with 6 micron mylar.

in general, we found older U47 microphones with PVC M7 capsule varied the most from sample to sample compared to U47's with more consistent mylar skinned K47 capsules which also provides a longer capsule life.

We have been using our AK47 capsule now in other tube microphones for several years with great results.  We select AK47 capsule for our CM47LE

Our CM47LE was recently compared by our friend Joseph Magee to two lovely U47 microphones at Oceanway Studios in Nashville and the results were more than favourable. 

INSIDE THE CM47LE

The Capsule

The CM47LE utilizes our custom vintage 47-style (K47) capsule like the one use in a classic U47 microphone circa 1959.  

Our AK47 capsule is designed with the same surface area, hole pattern, mylar thickness and frequency response as the original. Like the original capsule in a 1959 U47 our capsule's capacitance falls between 78-83pf.  Like a 1959 K47 pictured below it has a brass surround not nylon.

K47 capsule circuit 1959

Advanced Audio AK47 capsule

The Tube

The tube used is a GE/JAN 5654 tube which is a low voltage tube and a pentode like the original VF14M in th U47.  It is not a dual triode used by other U47 reproductions and even our slightly more modern sounding CM47VE.

Like the U47 we configure the 5654W as a single triode and drive a large footprint transformer with a 6.5:1 ratio.   We managed to locate a NOS VF14M tube and a transformer from a 1959 U47 and measure all the circuit parameter and duplicated it with a selected 5654w tube.

The Transformer

The CM47LE utilizes a custom would large footprint transformer with the exact core and electrical specifications as a 1959 BV08 from a U47.

The Cable

Every one of our professional 7 pin microphone cable is tested by us for phase, frequency loss and noise figures.

The Capacitors

The CM47LE uses polystyrene coupling capacitor, wima film bypass capacitors and a high tolerance Vishay output capacitor.

There are only three capacitors in the audio path.

 CONTENTS

Your CM47LE leatherette case includes; the CM47LE microphone, power supply with leather handle, IEC power cable, clip-on HD shock-mount, professional 7 pin microphone cable and wood microphone storage box fitted in the case.

POWERING UP A TUBE MICROPHONE

There is a vintage heavy duty toggle power switch which is located on the power supply with a large jewelled LED pilot light.

It is best to turn the power supply on after the 7 pin cable is connected between the microphone and the power supply.

There is a IEC power input connector located on the rear of the power supply.

The supplied IEC power cable can be connected here and then to the a/c mains outlet in your studio.

There is a 115v/230v Voltage Selector Switch on the rear.

*** It is very important that its NOT switched  to 115v when 230v is applied.  

This can cause immediate power supply failure.

Typically the voltage selector switch will be pre-set to the proper voltage of the country it is shipped to. 

Polar Patterns and the Multi-pattern Selector Switch.

The Advanced Audio CM47LE has a PASSIVE cardiod option which many U47 reproductions do not exhibit including our CM47VE which sounds great but does not share the subtle differences between passive and active capsule polarization found in the original U47 and our CM47LE .

Passive cardiod allows the capsule to exhibit 3db more output and the proximity effect is subtly wider.

On the CM47VE a toggle switch marked C or M allows for either the passive cardiod option or Multi-pattern which exhibits an active cardiod position as well as 8 other patterns controlled from a rotary switch.

The polar-pattern selection switch is located on the power supply and provides 9 different poor patterns . These patterns clock-wise are Omni, super wide cardiod, wider cardiod,  wide cardiod, cardiod, super cardiod, hyper cardiod and super hyper cardiiod and finally FIG 8. 

Some Notes on Multi-pattern microphone use

Polar Patterns and how to utilize them in recording situations.

There are several considerations for picking the right microphone for different recording situations. In the real-world there can are several factors that will affect the choice of microphones types and microphone polar patterns.  Polar patterns refers to graph looking at the microphones sensitivity from the top of the microphone in concentric circles. Understanding polar pattern be useful even for home recording studios with a limited budget.

Microphones can differ from one microphone to another in their choice of transducers, their frequency response and their polar pattern or pickup patterns. 

Changing the pick-up pattern can change the direction from which the microphones picks up the most full frequency audio waves. Microphone specifications typically come with detailed specific pattern related information.  This usually represents a two-dimensional view which shows the microphones sensitivity from different directions.

Types of Polar Patterns 

Omnidirectional - As the name itself suggests, an omni directional pick-up pattern captures sound waves from all directions equally, which makes them easy to place. They can be placed almost anywhere close to the audio source being recorded.  If you look at the polar pattern for an omni direction microphone it’s a perfect circle.  LDC microphones set to OMNI are often used in what’s called a Decca Tree for classical recording.  This microphone technique utilizes three LDC microphones set to OMNI.  The microphones are placed in a triangle about 2.5 metres above the conductor.  The centre microphone is about 1.5 metres in front of the conductor and the L/R microphones are 2 meters apart on each side of the conductor and these microphones are panned L/C/R. The centre microphone tends to fill in the centre (hole) of the L/R stereo image.  Omni is also used when you have a string section, or horn section or small vocal group gathered around one microphone.  It also an be useful in a well treated and quiet room in close on an acoustic instrument as there is no proximity effect (boom on the acoustic guitar) in OMNI a microphone can handle 6db higher SPL than in Cardiod.

Figure 8.  The majority of ribbon microphones have a Fig 8 response only.  This means the pickup sensitivity at the front and rear of the microphone is equal and the sound arriving on the L/R axis of the microphone is reduced.  All Advanced Audio LDC microphone except the CM47fet have the FIG 8 feature. Fig 8 can be useful when recording a duet with both singers recording at the same time. 

The vocalists can face each other to help vocal timing while the room sound is reduced because the audio sensitivity is greatly reduced on the sides.  Fig 8 can also be use to record acoustic and electric guitars when you want to have some room sound but control the balance between the direct sound a room sound.  This can be simply accomplished by moving the microphone away from or toward the source.  Another feature of FIG 8 that is very often over looked is its ability to capture the sound of an orchestra or choir with two Fig 8 microphones placed in a Blumlein pair on separate tracks.  

Both microphones are positioned in the same vertical plane and one microphone is positioned to pick-up Front Left and Rear Right the 2nd microphone picks up Front Right and Rear Left.  By moving the pair away from or closer to the source the amount of room sound is controlled.  On a recent live orchestra recording the writer used 3-Advanced Audio CM67se LDC tube microphones in OMNI configured as a Decca Tree.  These were paired with two CM251 LDC tube microphones back about 10 meters from the stage, set to FIG 8  and configured as a Blumlein pair. By bringing the Blumlein pair up in the mix, more room ambience could be added.  The Blumlein pair captures a very realistic audio picture of the ensemble in the room.  Moving the pair toward the source increases the direct sound and moving the pair away from the source result in more of the room sound.    

Two Fig 8 ribbon microphones in a real acoustic vocal chamber sound lovely.

Cardioid-according to Wikipedia is (from the Greek καρδία "heart")  It is defined as a plane curve traced by a point on the perimeter of a circle that is rolling around a fixed circle of  the same radius. defined as It is also defined as a vaguely heart-shaped microphone polar pattern. 

Cardiod microphones are sensitive to sounds  waves coming from the front but much less sensitive to sound waves reaching the rear of the microphone.  However, very low frequencies sound waves tend to be more omni directional so Cardiod do not reject low frequencies as well as voice frequencies.  Hand held vocal microphones are either cardiod, super cardiod or hyper cardiod.  In super-cardiod the heart shape is compressed  on the sides and the sensitivity drops more quickly each side of front and centre.  With hyper cardiod the sweet spot of maximum sensitivity is even narrower but this can be an asset in live venues with loud stage monitors and giant sound systems.

As, previously stated the CM47LE has fixed passive Cardiod or a Multi-pattern option where 9-pattern from Omni thru Cardiod to Fit 8 can be selected.

The makes the CM47Le a very versatile studio microphone.

Audio Output connection.

A standard 3 pin XLR male connector is located on the front of power supply. This can be connected to any professional preamp that has 40db of gain available and a 3- pin female XLR input connector.

              RESPONSE CURVE OF CM47LE IN CARDIOD